The invention relates to a torsional vibration damper and to a method for producing a bearing element for a bearing device for a torsional vibration damper.
Torsional vibration dampers of the generic type serve for damping torsional vibrations on a machine shaft—frequently an engine crankshaft. On the machine shaft, the damper housing of the torsional vibration damper is connected to a machine shaft—frequently an engine crankshaft—in a torsionally rigid manner, the torsional vibrations of which are to be dampened. The damper housing and the inertia ring follow the mean rotational speed of the machine shaft without slip. Their torsional vibrations by contrast, which are superimposed on the uniform rotation, are initially only superimposed on the damper housing. The inertia ring would rotate uniformly if a viscous fluid—for example a silicone oil—which fills the narrow shear gap, would not couple it to the damper housing. This coupling is elastic and subject to damping. Consequently, relative torsion angles of for example up to ±1 angular degree occur between damper housing and inertia ring in phase with the exciting shaft vibration. Since the inertia ring can thus rotate slightly relative to the damper housing in the damper housing chamber, at least one bearing device comprising one or more bearing elements is usually required for its mounting.
A substantial requirement in designing the bearing device of a torsional vibration damper is that the inertia ring located in the damper chamber is mounted so as to be freely moveable with the bearing device and that any collision with the damper chamber or with the damper housing, which forms the damper chamber, is excluded. This is realized by determining suitable nominal values and tolerances of inertia ring, bearing device and damper chamber. Frequently, the installation space for the torsional vibration damper on a motor or an internal combustion engine is limited. At the same time, because of the further development of motors or internal combustion engines, the function requirements of the torsional vibration damper increase.
In particular loosely inserted bearing elements have proved themselves as bearing device, which bearing elements form a sliding bearing between inertia ring and damper chamber. Accordingly it is known to combine a radial ring that is slotted at a point on the circumference thereof with two axial rings—EP 0 423 243—or to provide a multiplicity of axial guide platelets as bearing elements as bearing device—GB 1 307 607.
From DE 195 19 261 A1 a torsional vibration damper with a bearing device for guiding an inertia ring in a damper housing is known, in which as bearing device at least one bearing element that is L-shaped in the cross section is provided, which is inserted into the damper housing in such a manner that a radial bearing section of the L-shaped bearing element mounts and guides the inertia ring relative to the damper housing in the radial direction and that an axial bearing section of the L-shaped bearing element ensures an axial mounting and guiding. Between the inertia ring and the damper housing there are shear gaps which are filled with the viscous fluid. According to versions of this publication it is provided that two of the L-shaped bearing elements are arranged in the inner or outer circumferential gap of the inertia ring, or that one of the L-shaped bearing elements is combined with an axial strip. The L-shaped bearing elements can be designed as a circumferentially closed angular ring or designed to be slotted at a point on the circumference thereof.
From the generic DE 101 26 477 C1 it is known that the L-shaped bearing elements at a point on the circumference have a butt joint, which is bridged by at least one or more material webs, so that a circumferentially closed ring is formed. Preferentially, these material webs are configured in the manner of a predetermined breaking point so that they tear open or are elastically-plastically deformed when the bushing is subjected to a thermal increase in length. According to a further version of DE 101 26 477 C1, the butt joint is bridged by one or two material webs formed as tearing webs, which is/are aligned with the radial bearing arrangement and/or the axial bearing arrangement. It is likewise known that the butt joint is bridged by a material web designed as meander web and that the material web is a film web. According to the specification of DE 101 26 477 C1, the rings which are still circumferentially closed prior to the assembly can be mounted more easily as rings which are not circumferentially closed since they cannot become entangled. In addition, the predetermined breaking point makes it possible to employ the rings with slightly different bearing seat diameters. However, it is problematic that for bearing seat diameters that are not only slightly different, different bearing rings still have to be produced.
The object of the invention is to solve this problem.
The invention solves this object by providing a viscous torsional vibration damper having the following features: an annular damper housing, bounding a damper chamber; an inertia ring arranged in the damper chamber; a bearing device mounting the inertia ring in the damper housing, which comprises at least one or more bearing elements, wherein at least one of the bearing elements is formed as a ring that is not circumferentially closed in an assembled state; a shear gap filled with a viscous fluid between the inertia ring and the damper housing, wherein one or more axial bearing sections and one or more radial bearing sections are provided circumferentially distributed on the at least one bearing element formed as a ring that is not circumferentially closed, and wherein the bearing element formed as a ring that is not circumferentially closed is cut to length form a strip.
The length of the piece cut to length, which forms the bearing element, corresponds to the circumference of the bearing seat of the damper housing so that the bearing element on the one hand can be easily mounted to this bearing seat and on the other hand no gap that is too large forms between the ends of the bearing element, which would negatively affect the bearing function. “Not circumferentially closed” means that the ends of the bearing element are not connected to one another in a firmly bonded manner.
In addition, the invention provides a method for producing a bearing element for a bearing device of such a viscous torsional vibration damper, with the following steps:
Step A): providing a strip on which at least one or both of the following features are present: one or more axial bearing sections and one or more radial bearing sections and preferentially one or more webs, in particular radial webs; which if applicable—i.e. if present—connect the multiple axial bearing sections and/or radial bearing sections with one another;
Step B): cutting the bearing element to length from the provided strip; and
Step C): laying the bearing element cut to length from Step C) into a provided open damper housing on a bearing seat of the damper housing. In Step C) the bearing element cut to length—if it does not yet have the required radius—is additionally bent into the shape of a ring that is not circumferentially closed. Step C) can also comprise that the bearing element is placed on the bearing seat jointly with an inertia ring. Preferentially, however, the bearing element is placed into the damper housing before the inertia ring.
With the strip material or strip, bearing elements for bearing seats of different diameters can be realized. This saves tool costs since different tools for different bearing seat circumferences/diameters for producing the annular bearing elements of different circumference no longer have to be provided. The bearing element is simply cut to a length corresponding to the circumference of the bearing seat in a manner corresponding to the respective circumference of the bearing element. The production logistics are likewise simplified. This is accompanied by a saving of storage costs. In addition, prototype construction time is shortened and assembly errors are avoided. According to the invention, multiple axial bearing sections and multiple radial bearing sections are additionally provided on the at least one bearing element. This brings with it a number of advantages. Since the axial bearing sections and/or the radial bearing sections no longer extend over the entire or almost the entire circumference of the bearing element, but rather merely three or more axial and/or radial bearing sections are provided distributed over the circumference, the space filled in the shear gap by the respective bearing element is reduced and additional space is accordingly created, which can be filled by the viscous medium and in which a viscous coupling between the inertia ring and the damper housing is possible. This makes it possible to maximize the utilizable shear gap and to optimize the connection between the inertia ring and the damper housing. Sections on which during operation a slide bearing between the damper housing and the inertia ring can be continuously realized in the radial direction by these sections are described as the axial bearing sections and/or as the radial bearing sections.
It is additionally advantageous and practical to cut multiple of the bearing elements of a viscous torsional vibration damper to length in a simple manner from a single strip. However, strips of a different type can also be provided when the bearing elements cannot all be cut to length from the same strip, for example since their cross section is different.
In particular when a bearing element located, with respect to the inertia ring, axially outside is to be realized, the strip cut to length, because of its bending stiffness, hugs the outer damper housing towards the outside when it is inserted into the damper housing, so that the inertia ring in a step during the production of the torsional vibration damper can be easily placed into the damper housing.
According to an advantageous version, the at least one bearing element that is not circumferentially closed is cut to length from a strip which is provided as a straight strip. However, it is also advantageous when the at least one bearing element is cut to length from a bent strip, wherein the bend of the strip preferentially has a radius that is greater than that of the bearing seat. This strip can for example be provided on a reel like a continuous strip, the diameter of which reel is preferentially significantly larger than that of the bearing elements to be realized.
The strip can consist of plastic and can preferentially be provided in a cost-effective manner in an extrusion method.
It is advantageous to assemble the bearing element before the inertia ring. However, it is also conceivable—although less preferred—to place the bearing element against the inertia ring and to then place this preassembled unit in the still open damper housing. This version can be selected when the or a plurality of the bearing element(s) are to be assembled in inner corner regions of a housing.
Following this—for completing the production of the torsional vibration damper as such—the provided open damper housing is preferentially closed for example with a cover in a further step, wherein a filler opening for the viscous medium still remains. Following this, the viscous medium is filled in and the filler opening of the damper housing closed. A complete method for assembling a torsional vibration damper from the provided elements damper housing with cover, bearing device with bearing elements produced according to the above method, inertia ring and viscous medium is also realized in this manner.
Preferentially, at least three of the axial bearing sections and/or of the radial bearing sections are provided on the one or the two or more bearing elements, distributed over the circumference thereof.
In order to configure the regions which are additionally filled with the viscous medium to be large in size, the added circumferential length of the axial and/or radial bearing sections according to a preferred embodiment amounts to less than 50%, in particular less than 40% and particularly preferably less than 30% of the circumference of the entire bearing element.
Preferably, in each case circumferentially distributed the radial bearing sections and the axial bearing sections complement one another to form bearing sections that are L-shaped in the cross section, which are provided on the bearing element distributed over the circumference. By way of such L-shaped bearing sections, the inertia ring is particularly favorably centered and guided. Furthermore, the assembly with this configuration proves to be very simple since the bearing element configured in this manner can be easily placed into the shear gap before the damper housing that is generally initially open on one side for the assembly is closed once the bearing elements and the inertia ring have been inserted and filled with the viscous fluid at a filler opening still to be closed later on.
For realizing a good bearing it is practical when two of the bearing elements are arranged in the damper chamber. Although more of the bearing elements can be theoretically provided, two bearing elements for mounting the inertia ring are generally sufficient. This also makes the assembly simple.
It is advantageous if the damper chamber has a substantially rectangular cross section with inner and outer corner regions. These corner regions then preferentially and simply form the bearing seats for the bearing elements. Then, according to one version, two of the bearing elements can be arranged in the outer corner regions of the damper chamber between the damper housing and the inertia ring. This configuration can be assembled particularly easily. This configuration is advantageous but not mandatory. Other cross sections such as C-shapes and the like are also conceivable.
Alternatively, two of the bearing elements can be arranged in the inner corner regions of the damper chamber between the damper housing and the inertia ring.
Finally it is also conceivable that one of the bearing elements is arranged in one of the outer corner regions and a further one of the bearing elements is arranged in one of the inner corner regions of the damper chamber between the damper housing and the inertia ring. Here it is preferred if the bearing elements are arranged in corner regions which are located diagonally opposite one another in the damper chamber since this favorably centers the inertia ring.
Preferentially, the bearing elements of the bearing device are arranged between the damper housing and the inertia ring without preload in order to ensure a good mounting. This is particularly preferred since in this manner a good mounting is ensured. Plastic is preferentially employed as material for the bearing elements of the bearing device. The viscous fluid is preferably a silicone oil. However, in individual cases, the bearing elements can also be assembled with preload.
Within the scope of the invention an embodiment of the bearing device can also be realized in which at least one of the bearing elements merely comprises one radial bearing section and radial webs of smaller strip thickness connecting these. These bearing elements are then preferably—but not mandatorily—combined with bearing elements with which in each case distributed over the circumference the radial bearing sections and the axial bearing sections complement one another to form bearing sections that are L-shaped in the cross section. Then, one of the bearing elements guides the ring preferentially in the radial and the axial direction and the other one guides the inertia ring only in one of these directions.